Marking pen



FIG. 1 is a front perspective view of a marking pen showing my new design.

FIG. 2 is a front elevation view of FIG. 1, a back elevation view being a mirror image thereof.

FIG. 3 is a left side elevation view of FIG. 1, a right side elevation view being a mirror image thereof; and,

FIG. 4 is a top plan view of FIG. 1.

The broken lines in the drawings are included to show portions of the marking pen that form no part of the claimed design. 

CLAIM The ornamental design for a marking pen, as shown and described. 